Rhizoctonia stem rot is a condition of plants in which Rhizoctonia solani Kuhn [Teleomorph=Thanatephorus cucumeris (Frank) Donk], colonizes in the stem and roots of a plant. Stem rot is a serious disease which can result in stunting or die back of mature plants later in production. Jones, R. K., North Carolina Flower Growers' Bulletin, 35(4):6-11 (1990); Strider, D. L. et al., Poinsettias in Diseases of Floral Crops Volume 2, 351-403 (D. L. Strider, ed., Praeger Publishers, New York, 1985). Stem rot can be detrimental during all stages of plant growth, but is particularly favored under the conditions that prevail during late-summer rooting. Consequently, the prevention or control of stem rot during the rooting period is critical. Ecke, P., Jr., Matkin, O. A., and Hartley, D. E. (eds). The Poinsettia Manual. (Paul Ecke Poinsettias. Encinitas, Calif., 1990).
Control of stem rot is dependent on cultural practices and the use of effective chemical fungicides. Powell, C. C., Jr., Plant Dis 72:693-695 (1988); Snowden, S. E. et al., Fungic and Nematic Tests 38:182 (1982). The use of clean, sterilized pots, pasteurized soil or propagation medium, disease free stock plants, and sanitary greenhouse practices combined with repeated applications of fungicides such as benomyl [(methyl 1-(butylcarbamoyl)-2-benzimidazole-carbamate] or PCNB (pentachloronitrobenzene) can reduce severity and spread of stem rot. See Snowden et al., supra, Bolton, A. T., Canadian J Plant Path. 5:181-184 (1983). The disease, however, continues to occur annually at endemic and occasionally epidemic levels. This is attributed to poor management, time, labor, and expense involved in the implementation of control measures and growing fears and constraints related to chemical pesticide use. See Tweedy, B. G, The future of chemicals for controlling plant diseases in Challenging Problems in Plant Health 405-415 (T. Kommedahl and P. H. Williams, eds. The American Phytopathological Society. St. Paul, Minn. 1983); see also Urbain, C. D., Farm Jour 110(13):15-16 (1986). For example, fungicides, particularly when misused, can pose environmental and health related risks. Food and groundwater contamination, residue carryover, applicator exposure, plant injury, and buildup of pest resistance due to pesticides have cast doubts about their future use. See Urbain, supra; Staub, T. et al., Plant Dis 68(12):1026-1031 (1984); Powell, C. C., Jr., Plant Dis 72:693-695 (1988).
These problems have stimulated interest in alternative means of disease control, such as biological control. Cook, R. J. et al., Perspectives in The Nature and Practice of Biological Control of Plant Pathogens 426-444 (R. J. Cook and K. F. Baker, eds., American Phytopathological Society, St. Paul, Minn. 1983); Baker, K. F., The future of biological and cultural control of plant disease in Challenging Problems in Plant Health 422-430 (T. Kommedah. and P. H. Williams, eds., American Phytopathological Society, St. Paul, Minn. 1983). Biological control of plant diseases with antagonistic microorganisms has potential; these tactics can be safe, effective, and economical. Efforts to control R. solani with strains of fungi, bacteria, or actinomycetes have shown marginal success; however, none have been developed for use on a practical basis. See Beagle-Ristaino, J. E. et al., Phytopathology 75:560-564 (1985); Kwok, O. C. H. et al., Phytopathology 77:1206-1212 (1987); Rothrock, C. S. et al., Can. J. Microbiol 30:1440-1447 (1984).
Accordingly, it is an object of the present invention to provide a method for treating stem rot of plants through the use of a biocontrol agent. It is a further object to provide the aforementioned biocontrol agent.